Electric switch



Aug. 22, 1944. H. OLKEN ELECTRIC SWITCH Filed March 7, 1942 3)WMHIOD H YMAN ULKEN Q ff! W 3394 3 Q" Patented Aug. 22, 1944 UNITED STATES PATENT OFFICE ELECTRIC SWITCH Hyman Olken, Washington, D. 0.

Application March 7, 1942, Serial No. 433,809

7 Claims.

My invention relates to electric switches, more especially to pressure-actuated switch units, and to a method of producing the same.

An object of my invention is the provision of pressure-actuated electric switches of the Bourdon spring type; which are capable of being adjusted to a high degree of sensitivity, without danger of injury to working parts; which possess great reliability in operation, being responsive to slight pressure; and which accomplish switching operations without interference from dirt, moisture, and the like.

Another object of my invention is the provision in an economical manner of sensitive, pressure-operated switch units comprising adjustable electrical contact elements, sealed in a casing; which units are capable of adjustment without disturbing the casing seal; which possess a minimum of working parts; and which in operation exhibit great stability and high efliciency.

Other objects and advantages, in part, will be obvious and, in part, pointed out hereinafter.

My invention, accordingly, resides in the several elements, features of construction, and operational steps, and the combination of each of the same with one or more of the others, all as pointed out hereinafter, and the scope of the application of which is set forth in the appended claims.

In the accompanying drawing illustrating certain features of my invention,

Fig. 1 is a diagrammatic view of an assembled, pressure-actuated switch unit.

Figs. 2 and 3 are diagrammatic views of several other pressure-actuated switch units, having modified switch contact elements.

Fig. 4 shows a modified pressure fluid reservoir, for pressure-actuated switches.

As conducive to a clearer understanding of my invention, it should be noted at this point, that pressure-actuated electric switches are considerably in demand, particularly for use in electric control devices employed in regulating electrically-operated apparatus. There are electrically-operated devices employed, as for example, in the production of heat, pressure or electric power, and in the electric circuit of such devices, it has been the practice to provide automatic control means for regualting or limiting energy output. The control conveniently includes a pressure-actuated switch, responding directly or indirectly to the output energy of the electrically-operated apparatus. In way of further illustration, pressure-actuated switches also ZOO-431.8)

are of value in the remote control of certain types of electrical apparatus, where switch-operating pressure is governed by a pressure treadle, solenoid, voice coil, or the like.

Of the pressure-actuated switches in the prior art, as for example, the Bourdon tube type switches, certain are found to be objectionable in many fields of use, particularly because of their lack of sensitivity to pressure change. Such switches are not reliable where small pressure differences are depended upon to achieve switching functions. Other pressure-actuated switches of the prior art fail to respond to a given actuating influence in a consistent manner, under varying temperature conditions. This is particularly true of switches of the Bourdon tube or spring type, wherein varying pressure of fluid in the tube is responsible for achieving make and break switching operations. Pressure of fluid contained within the Bourdon tube varies with temperature to bring about undesired displacement of the tube, and thus makes the switch contacts more or less responsive to pressure control.

It is diflicult to adjust the heretofore known Bourdon tube, pressure-actuated switches, so that circuit making or circuit breaking is delayed until a desired switch-operating pressure condition is achieved. Where a protective switch casing is employed, the problem of switch contact adjustment becomes more acute, for it usually is not practical to disturb the casing, in order to reach the contacts for making adjustment. Yet, it is quite important to protect the working parts of the switches, particularly the switch contacts, from atmospheric moisture and dirt, so as to prevent the switch contacts from arcing and corroding.

An outstanding object of my invention, accordingly, is the provision of a pressure-actuated electric switch of the Bourdon tube type, having switch contact elements and included contact points, encased in a hermetically-sealed casing, which is capable of being adjusted from without the protective casing so as to delay circuitmaking or circuit-breaking action between switch contact points, until a desired actuatingpressure condition is achieved, and which is responsive in a uniform manner to a given operating pressure, under varying temperature conditions.

As illustrative of the production of my pressure-actuated switch units, I make or procure a glass hood H11, and a glass stem or base l2b, having spaced, open tip portions lZd, 12c and i2 (See Fig. 1). I align hollow, metallic, terminal pieces I and II with the open tips I2e and I2j of base I21), and secure the terminals to the tips, by forming metal to glass seals in any wellknown manner. The glass stem is ready to receive my switch contact structure.

In erecting the switch contact elements, I insert one end of an electrically-conductive contact element I3 through glass stem tip I2f and into the hollow portion of terminal I0, to a point well past the metal to glass seal. A bi-metallic element I 3a forms a part of the free end of contact element I3 and includes a switch contact point I3b. Solder is poured between the contact element and the inner wall of terminal I!) to a point considerably short of the metal to glass seal. The solder forms an electricallyconductive, fiuid-tight seal, and also serves to hold the contact element in erected position.

Likewise, I insert an electrically-conductive Bourdon tube contact element M through the glass stem tip I 2e and into the hollow portion of the terminal I I to a. point well past the metal to glass seal. A contact point Mb, included on the opposite closed end of the Bourdon tube contact element, is brought adjacent to contact point I3b of element I3, as for example, to closing position therewith. Solder is poured between the Bourdon tube contact element and the inner wall of terminal II to a point considerably short of the metal to glass seal, so as to form a fluid-tight seal in the terminal, Without interfering with the metal to glass seal. In pouring the solder, care is exercised to avoid covering the open end Me of the Bourdon tube switch contact element.

The glass hood I 2a is positioned over the erected contact structure and is brought into fitting relationship with stem I2b at I2c where an airtight, glass to glass seal is formed, in any wellknown manner. The resulting glass casing I2 then is evacuated through tip I 2d or is filled through the same tip with inert gas, such as nitrogen or helium. Evacuation or filling of the tube is carried out to such degree of pressure, as to prevent arcing across the switch contact points when the contact points are open. The open tip I2d of the glass casing I2 then is sealed off.

An open outer end of terminal II is secured by air-tight seal to a hollow cylindrical fitting I6, having a set-screw IBc threaded through the wall thereof and a diaphragm face Hie. The cylindrical fitting provides a fluid reservoir I6b which communicates with the bore Ma of the Bourdon tube. I remove the screw IBc from the cylindrical fitting and fill the reservoir [6b and Bourdon tube bore Ma with fluid, such as oil. The set-screw is reinserted and the switch is ready for use.

Where desired, my switch unit is assembled in a heat or shock-resistant casing IT, or after assembly, is inserted in such casing. Any suit able mounting means is employed to hold the switch unit in position within the casing.

In order to achieve more complete degassification of casing I2, I find it helpful to heat the casing during the evacuation step. Gasses occluded in the casing wall, accordingly, are freed for removal from the casing. It also is helpful to employ a chemical getter compound in the casing, for reaction with gases remaining after evacuation.

It will be understood that where practical, one of the hollow tips [2 or [26 may form a part of glass hood I 2a, rather than base I2b. Where such is the case, corresponding terminal ID or II is sealed thereto by metal to glass seal, and the switch unit then is assembled in the manner prescribed hereinbefore. It will be appreciated, further, that where practical, the switch contacts may be brazed into the terminal pieces, before sealing the terminals to the glass stem I2b or to the glass hood l2a. The casing elements I2a and [2b, moreover, may be made of ceramic material, Bakelite, or even metal, if proper insulation between terminals I0 and II is provided. Further advantage is achieved at times by mounting the terminal I I and fitting I6 as an integral unit on the casing base portion I 2b, or by hermetically sealing the Bourdon tube M and fitting I6 as an intergral unit to terminal II.

The operation of my pressure responsive switch unit is quite simple. Upon the application of external pressure to the face of diaphragm IBe, fluid pressure in reservoir I6b and bore Ma increases and the curved Bourdon fluid-spring tends to straighten. Contact point Mb, accordingly, is displaced from contact point I3b and an electric circuit traced from a suitable source of power (not shown) to terminal I0, through contact element I3, contact points I3b, Mb, Bourdon tube M, terminal II and back to the source is broken. As external pressure upon diaphragm I6e decreases contact point Mb approaches contact point I3'b until the points meet and thus the circuit once more is closed.

By assuming for a moment that external pressure has been withdrawn from the face of diaphragm IBe, it can be seen that switch contact points I3b and Mb may, depending upon their relative adjustment, rest together under considerable force exerted by tube or spring I5. In order to alleviate this pressure, screw IE0 is tightened down farther into the fluid chamber I 82). Fluid pressure within the Bourdon tube, accordingly, increases and contact point Mb tends to move away from contact point I3b.

Pressure between the points diminishes and a lighter external pressure is required upon the face of diaphragm I6e to bring about actual separation of the points. Thus, switch sensitivity to pressure applied to diaphragm IBe is regulated by adjustment of set-screw I60. This adjustment, it will be noted, is accomplished from without the hermetically-sealed casing I2 and in no way disturbs the casing or its seal.

Assume now that set-screw I60 has been adjusted so as to make the switch points I3?) and Mb open under a given pressure applied to diaphragm ISe. This adjustment is sufficient to ensure reliable switch operation under constant temperature conditions, but upon a change in temperature, pressure of fluid in the reservoir Hub and tube bore Ma is altered. Bourdon tube I4, accordingly, is displaced in undesired amount, and thus switch sensitivity is affected by temperature change. In order to compensate for the effect of temperature, the bi-metallic portion !3a of switch contact element I3 is provided with a displacement constant, substantially equal to that of the Bourdon tube. Any displacement of contact point Mb to or from point 13b, caused by temperature change, accordingly, is met by a substantially equal displacement, in direction and amount, of point I3b supported on deflecting i-metallic element l3a.

Figure 2 illustrates a modified form of my invention, wherein a pressure-actuated switch Fig. 4), a heat bulb I I6 disposed without hermeti unit assembled, for example, in accordance with the method hereinbefore described with respect to the unit of Fig. l, is provided with switch contact points, which normally are open. A switch contact point I 412, provided on displaceable closed end of Bourdon tube I4, normally forms a short 'air-gap'with contact point I3b. Point I 3b is supported at one end of bi-metallic element I3a, both of which form. parts of electrically-conductive contact element I3. Ahermetically-sealed casing I2, having electrically separate metallic terminals I and II sealed thereto, houses the switch element assembly just described. The end of contact element I3 opposite contact point I3b is. connected within terminal I 0' by means of solder or the like. Bourdon tube I4 is provided with an open bore l4a sealed off by air-tight, electrically-conductive, seal I 5 from the interior of casing I2. A cylindrical fitting I6 is threaded or is otherwise tightly fastened to the outer end of terminal II, and forms a fluid chamber H31), in open communication with the interior of Bourdon tube I4. The chamber and tube are filled with fluid such as oil, for example, through set-screw opening IIid. Set-screw 16c is placed in the opening I6d and the switch unit is ready for use Upon application of external pressure to the diaphragm Ifie, fluid pressure in reservoir I61) and Bourdon tube I4 increases, and the Bourdon tube tends to straighten within the sealed casing I2. Contact point 141), accordingly, is displaced toward point I31); and where pressure on diaphragm I5e is sufiiciently high, the points close. Upon closure of the points, a circuit is completed from a source of power (not shown) to terminal l8, across contact element I3, bimetallic element his, contact points I31), I 41), Bourdon tube I4, terminal II, and back to the source. Where pressure on diaphragm I6e' decreases, contact point I lb moves away from contact point I31) and the circuit just described is broken.

Adjustment of the normal air-gap existing between switch contacts is made by altering the protruding length of set-screw IBc in fluid chamber I61). To prevent the adjusted air-gap from being afiected by temperature variations, the bimetallic portion I3a of contact element I3 is so constructed as to have a temperature displacement constant substantially equal to that of the Bourdon tube. Any undesired displacement of contact I4b' caused by temperature change, accordingly, is met by a substantially equal displacement, in direction andamount, of contact point I3b' supported on deflecting bi-metallic element I3a.

It will be understood that where my switch units are employed under substantially constant temperature conditions, satisfactory switching operation is achieved by replacing the bi-metallic element I311 or lea with an ordinary metallic piece, or by using a single metallic contact element extending from switch terminal Ill or I0, and including contact i373 or I37). Where such is done, switch operation remains the same as described hereinbefore, except of course, the temperature compensating feature is omitted.

Likewise, where the temperature compensating feature of my invention is omitted, the switch units make ideal heat responsive unit. In lieu of relying upon external pressure as a switchactuating force, external heat or cold is the controlling factor in altering pressure of fluid within the Bourdon tube. In way of illustration (see cally-sealed casing I I2 is connected with Bourdon tube I I4 sealed by air-tight seal in terminal III. In such uses, the heat bulb and Bourdon tube preferably are filled with fluid having a high coflicient of expansion. Switch sensitivity to external temperature change is adjusted, for example, by set-screw IIGc from without the hermetically-sealed casing as before.

A still further modified form of my invention is illustrated in Fig. 3 where a Bourdon tube I4", connected with hollow terminal II" and having bore I4a" communicating with the interior of cylindrical fitting I6", extends into hermeticallysealed, evacuated or pressure-filled casing I2. The tube is provided at its free end with an electrical contact point I4b. Fluid chamber IIib and tube bore I4a" are filled with fluid, such as oil set-screw I60", threaded in opening Ilia" of casing I6, passes into the fluid chamber IIib". Bourdon tube I3, sealed at both ends and also containing fluid such as oil, is mounted in hollow terminal I0" and extends into hermetically-sealed casing I2", in substantially parallel relation with tube I4. The Bourdon tubes are constructed similarly and contain like fluids, so as to have the same displacement characteristics under external temperature change. A metallic piece I3a" carrying contact point I31), is connected with the free end of Bourdon tube I3". Although contact point I32) normally is separated from point I 4b, it will be understood that by modified arrangement, the points may normally assume closed position (as in Fig. 2).

By applying external pressure to face I6e", fluid pressure in chamber I61) and tube bore Ma", increases, causing the Bourdon tube I4" to straighten slightly. Contact I4b, therefore, closes on contact I3'o and a circuit including terminal Ill, Bourdon tube I3", metallic piece I3a", points I31)", Mb", Bourdon tube I4" and terminal II", is closed. Reduction of external pressure similarly is responsible for movement of Bourdon tube in an opposite direction, whereby contact Mb" is displaced from contact I31)" and the circuit is broken.

The width of normal air-gap between the switch contact points is adjusted by means of setscrew I50". As the protruding length of screw I6c in fluid chamber IE2)" is increased, pressure of fluid in the chamber and in Bourdon tube I4" increases. Bourdon tube I4" tends to straighten under the increased fluid pressure and contact point 54b is carried toward contact I372. Similar-ly, the air-gap between points is increased by shortening the protruding length. of screw I60 in chamber 66b. Temperature variation has little effect upon an adjusted spacing of switch contacts. Both Bourdon tubes I3" and I4" are displaced substantially an equal amount with respect to direction and distance, when fluid in the tube is subjected to an increasing temperature.

I find that where the casing of any one of my pressure-actuated switch units is filled with inert gas under considerable pressure, or is evacuated to a considerable degree, the switch contacts contained therein are capable of being adjusted for highly sensitive operation. The opening and closing range of switch contact movement is di minished to a very small value, without danger of arcing. The contact points need, for example, only /1 inch separation per 5,000 volts in vacuum. Such highly refined adjustment of the contact points of my switches, it will be noted, is accomplished by means disposed externally of the switch casing, and the refined adjustment is maintained accurately under varying temperature conditions, all as set forth hereinbeiore.

Thus it will be seen that there has been provided in this invention, encased pressure-actuated switch units and a method of producing the same, in which the various objects hereinbefore noted, together with many thoroughly practical advantages, are successfully achieved. It will be seen that the switch units provided are strong, durable and compact of construction, and that they are adapted for uses requiring great sensitivity and high eiliciency of operation.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments hereinbefore set forth, it will be understood that all matter described hereinbefore, or shown in the accompanying drawing, is to be interpreted as illustrative, and not in a limiting sense.

I claim:

1. A pressure-actuated switch unit of the character described, comprising in combination, a hermetically-sealed evacuated switch casing supporting a switch contact element and included contact point therewithin; and a fluid-filled Bourdon tube sealed into said casing with a portion thereof extending exteriorly of said casing and a portion projecting into the evacuated casing with a curved fluid spring extension having a contact element mounted thereon including a contact point adjacent said other contact point but insulated therefrom.

2. A pressure-actuated switch unit of the character described, comprising, in combination, a hermetically-sealed switch casing supporting a switch contact element and included contact point therewithin; and a fluid-filled Bourdon tube having a reservoir with a pressure dia phragm connected to the end of the Bourdon tube, said end being disposed exteriorly of said casing with a portion sealed into said casing and a portion projecting into the casing with a curved fluid spring extension having a contact element mounted thereon including a contact point adjacent said other contact point, said diaphragm adapted to be actuated upon for operating said switch.

3. A pressure-actuated switch unit of the character described, comprising, in combination, a hermetically-sealed casing; a fluid-filled Bourdon tube sealed into said casing with a portion thereof disposed exteriorly of said casing, and a portion projecting into said casing with a curved fluid-spring extension having a contact element mounted thereon including a contact point, said curved fluid-spring extension and included contact point being displaceable under varying temperature condition; and a thermally displaceable second switch contact element connected with said casing in electrically separate relationship to said first switch contact element, and including a contact point within the casing adjacent said first contact point, said contact points being substantially equally displaceable in direction and amount under variable temperature conditions whereby pressure contact adjustment on said switch contact is made.

4. A pressure-actuated switch unit of the character described, comprising, in combination, a hermetically-sealed switch casing supporting a switch contact element and included contact point therewithin; a fluid-filled Bourdon tube switch contact element connected with said casing in electrically separate relationship to said first switch contact element, and having a portion thereof disposed exteriorly of said casing, and protruding into the casing in a curved nuid spring extension including a contact point normally closed upon said other contact point; said fluid-spring included contact being displaceable from said other contact point under substantial change in pressure of fluid within the Bourdon tube; and means cooperating with the exterior portion of said Bourdon tube contact element for efiecting slight change in fluid pressure therewithin and thus slightly altering the presure required to open said switch contacts.

5. A pressure-actuated switch unit of the character described, comprising, in combination, a hermetically-sealed casing; a fluid-filled Bourdon tube switch contact element connected with said casing, and having a portion thereof disposed exteriorly of said casing, and protruding into said casing in a curved fluid-spring extension including a contact point, said curved fluid-spring extension and included contact point being displaceable under varying temperature condition; a thermally displaceable second switch contact element connected with said casing in electrically separate relationship to said first switch contact element, and including a contact point within the casing adjacent said first contact point, said contact points being substantially equally displaceable in direction and amount under variable temperature condition; and means cooperating with the Bourdon tube switch contact element outside said casing for making slight adjustments in pressure of fluid therein.

6. A pressure-actuated switch unit of the character described, comprising, in combination, a hermetically-sealed casing; two fluid-filled Bourdon tube switch contact elements connected in separate electrical relationship with said casing and protruding therein in curved fluidspring extensions including contact points disposed in adjacent relationship; at least one of said Bourdon tube contact supports having a portion thereof disposed exteriorly of said casing and having a pressure diaphragm secured thereto.

'7. A pressure-actuated switch unit of the character described, comprising, in combination, a hermetically sealed switch casing supporting a switch contact element and included contact point therewithin; and a fluid filled Bourdon tube having a reservoir with a pressure diaphragm connected to the end of the Bourdon tube, said end being disposed exteriorly of said casing with a portion sealed into said casing and a portion projecting into the casing with a curved fluid spring extension having a contact element mounted thereon including a contact point ad jacent said other contact point, said diaphragm adapted to be actuated upon for operating said switch, and means varying the effective reservoir capacity to adjust initially the position of the contact point carried by the Bourdon tube within the vessel.

HYMAN OLKEN. 

